This invention relates to the art of increasing the filling powder of tobacco. More particularly, this invention relates to a process whereby the filling power of tobacco is increased by contacting the tobacco with supersaturated aqueous calcium citrate and then drying the tobacco by heating.
During curing, the moisture content of tobacco leaves is greatly reduced resulting in shrinkage of the leaf structure and a decrease in filling power. Additionally, the shredding or cutting techniques employed to convert cured tobacco leaves into filler may result in some lamination and compression of the tobacco, thereby decreasing the filling power even further. Many processes have been devised for increasing the filling power of cured tobacco for reasons well known in the art.
The heretofore known processes may be broadly characterized as expansion or stiffening. Expansion involves penetration or impregnation of the tobacco with impregnants (blowing or puffing agents), which when removed during the subsequent expansion step, generate elevated pressure in and expand the tobacco. Among the impregnants which have been employed are pressurized steam, air, water, organic solvents, ammonia, carbon dioxide, combinations of ammonia and carbon dioxide, and compounds capable of liberating a gas when subjected to chemical decomposition, as by heating. Among the means disclosed for removing the impregnant to expand the cell walls are a sudden reduction in pressure, freeze-drying, convection heating, radiant transfer (infrared) and the application of a microwave field.
It is also known in the art to increase the filling power of tobacco by stiffening the tobacco. Such stiffening treatment may be applied in conjunction with an expansion process to maintain the tobacco in its expanded state after removal of the impregnant. One such process involves impregnating the tobacco with a solution (usually aqueous) of multivalent metal or organic acid salts, and then drying the tobacco. The tobacco is expanded by means of the solvent and, upon drying, the various salts and ions bind to the pectinaceous materials naturally occurring within tobacco to stiffen the pectins and prevent the tobacco from returning to its original unexpanded form. An increase in filling power of 5 to 25% is reported. The multivalent metal and organic acid salts specifically disclosed for use in this process are calcium acetate, calcium gluconate, calcium levulinate, aluminum citrate, potassium titanium oxalate, aluminum sulfate, potassium aluminum sulfate, ammonium aluminum sulfate, magnesium sulfate, ammonium magnesium sulfate, ferrous sulfate, hydrated ammonium aluminum sulfate, hydrated potassium aluminum sulfate, hydrated aluminum sulfate, hydrated potassium titanium oxalate, and calcium sulfamate. The amount of the multivalent metal or organic acid salts applied to the tobacco ranges from 0.2% to 7.5% by weight of the dry tobacco.
Other stiffening agents known in the art include polyfunctional carboxylic acids, carbonyl chloride, aldehydes, diammonium phosphate, ketenes, lactones and aldehydic and keto sugars. To achieve significant increases in filling power with these stiffening agents, the use of high temperatures, non-aqueous volatile organic solvents, and expansion techniques are disclosed.
The addition of alkaline earth metal salts for improving smoking characteristics is known in the art. Generally, the salts constitute 0.1 to 0.5% by weight of the final product.
It is also known to improve the mildness of reconstituted tobacco by adding a combination of carbon and alkaline earth oxides, bicarbonates, or hydroxides to the filler. Calcium and magnesium compounds are said to give good results. The carbon and alkaline earth additives constitute 2 to 50% by weight of the final product.